A101012 Indices of primes in sequence defined by A(0) = 91, A(n) = 10*A(n-1) + 51 for n > 0.

2, 3, 4, 5, 7, 15, 33, 40, 51, 88, 104, 321, 634, 939, 943, 1130, 1197, 1742, 1871, 37913, 41655, 90095, 99473

Offset

1,1

Comments

Numbers n such that (870*10^n - 51)/9 is prime.

Numbers n such that digit 9 followed by n >= 0 occurrences of digit 6 followed by digit 1 is prime.

Numbers corresponding to terms <= 1130 are certified primes.

a(24) > 10^5. - Robert Price, Jan 10 2017

References

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Links

Table of n, a(n) for n=1..23.

Makoto Kamada, Prime numbers of the form 966...661.

Index entries for primes involving repunits.

Formula

a(n) = A103103(n) - 1.

Example

96661 is prime, hence 3 is a term.

Mathematica

Select[Range[0, 100000], PrimeQ[(290*10^# - 17)/3] &] (* Robert Price, Jan 10 2017 *)

Prog

(PARI) a=91; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+51)
(PARI) for(n=0, 1500, if(isprime((870*10^n-51)/9), print1(n, ", ")))

Crossrefs

Cf. A000533, A002275, A103103.

Sequence in context: A131023 A069514 A249155 * A373961 A048659 A065774

Adjacent sequences: A101009 A101010 A101011 * A101013 A101014 A101015

Keyword

nonn,hard,more

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Nov 27 2004

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(20)-a(21) from Kamada data by Ray Chandler, Apr 28 2015

a(22)-a(23) from Robert Price, Jan 10 2017

Status

approved